This invention relates to the coupling of sections of pipe by the use of coupling housings engaging grooves in the pipe and is particularly concerned with improvements in the gaskets employed for sealing the joint between the pipe ends.
In the coupling of sections of pipe employing coupling housings bridging the gap between the pipe ends, which housings engage grooves in the pipe exteriors and contain pressure-responsive gaskets bridging the gap, the pressure of the fluid in the pipe is effective to assist in sealing the joint. In order that it may do so, it is common to employ gaskets of C-shape in cross section and to couple the pipes with the ends thereof spaced a small distance apart providing for flexibility in the joint, thus leaving a path between the interior of the pipes and the interior of the gasket for transmission of the pressure to the gasket. When the "C" shape is in position on the pipe ends, the opening in the "C" sits over the gap between the ends. This allows the internal pressure to enter the gasket cavity and force the gasket lips down onto the pipe surfaces for increased tightness. This cavity feature, while being effective in increased sealing qualities presents a problem in certain piping services. Such services generally involve the conveyance of fluids carrying particulate matter or conveyance of finely granulated solids where the solids tend to fill the gasket cavity, thereby limiting its function to flex. This, in turn reduces the ability of the pipe ends to articulate when temperature changes or other forces are present. Such service requirements for piping joints are found in power piping systems where powdered fossil fuel is pumped through piping into steam generating furnaces. (While operating temperatures in these piping systems are ambient, periodic flashbacks from the furnace cause the temperature inside the piping to increase drastically and, in many instances, beyond the maximum temperature the gasket elastomeric material can withstand.) It is undesirable to allow the product flowing through the pipe to gather in the hollow of the gasket, commonly referred to as the "well".
There are gasket sections offered that have modified "C" sections to eliminate the gasket cavity. These sections are designed to fill the space inside the coupling cavity and, in so doing, become a solid unyielding section without the necessary ability to allow the adjoining pipe ends to flex, at least not without the risk of damaging the elastomeric material of the gasket. Furthermore, such sections have little or no compensating features (because solid elastomerics are practically incompressable) for accommodating reductions in section due to over heating conditions which cause material degradation. One such modified section is covered by U.S. Pat. No. 3,351,352.